Photoredox Imino Functionalizations of Olefins

Abstract

Shown herein is that polyfunctionalized nitrogen heterocycles can be easily prepared by a visible-light-mediated radical cascade process. This divergent strategy features the oxidative generation of iminyl radicals and subsequent cyclization/radical trapping, which allows the effective construction of highly functionalized heterocycles. The reactions proceed efficiently at room temperature, utilize an organic photocatalyst, use simple and readily available materials, and generate, in a single step, valuable building blocks that would be difficult to prepare by other methods.

Keywords: cyclization; nitrogen heterocycles; photochemistry; radicals; reaction mechanisms.

Scheme 1

Nitrogen heterocycles and mechanistic analysis of the divergent functionalization processes developed in this work.

Scheme 2

Substrate design and electrochemical studies.

Scheme 3

Scope of the imino functionalization strategy. Base used: [a] 2,6‐lutidine, [b] K₂CO₃, [c] Cs₂CO₃, [d] CsOBz. Solvent used: [e] CH₂Cl₂, [f] Toluene, [g] iPrOH, [h] MeOH, [i] Hexafluoroisopropanol, [j] CH₃CN/H₂O (2:1). Equivalents of X‐Y: [k] 3.0 equiv, [n] 4.0 equiv. Bn=benzyl, TIPS=triisopropylsilyl.

Scheme 4

Reaction scope. See Scheme 3 for solvent and base used in each imino functionalization reaction.17